Electronic ballast circuits are required to provide AC (alternating current) power to a gas discharge lamp in a manner which is uniform over time (i.e. has low ripple in the lamp current envelope) and such that the current drawn from the AC power line is sinusoidal and in phase with the line voltage. In addition, it is desirable that the cost of the components used to achieve this should be relatively low. The most expensive components used in an electronic ballast circuit are the magnetic components which are usually transformers or inductors. If the ballast is operating at a high frequency compared to the AC line frequency, then a so called EMI (electromagnetic interference) filter to prevent electronic noise from escaping onto the AC power line is usually needed. In order to force a sinusoidal current through a gas discharge lamp, one other magnetic component is needed to resonate with a resonant capacitor and produce the sinusoidal current waveforms desired. Although non-power factor corrected ballasts have previously been described using only these two transformers, it is desirable for purposes of cost reduction to have a power factor corrected ballast which functions using only two transformers .